Section 3 Rule applicability

3.1.1  Trimaran. A trimaran is defined as a vessel with three hulls of displacement form, a main centre hull stabilised by two much smaller side hulls, with the displacement of each side hull not exceeding six per cent of the total vessel displacement. The Trimaran Rules may also apply to vessels with three hulls of planing or semi-planing form or to vessels with five hulls, described as pentamarans. In these cases, special arrangement must be made with LR.

3.1.2  Vessel size. The Trimaran Rules apply to vessels whose Rule length, L _R, as defined in Vol 1, Pt 1, Ch 1, 5.2 Principal particulars 5.2.2, is between 70 m and 250 m. Vessels whose Rule Length is outside these limits will be specially considered.

3.1.3  Material. The material type applicable to vessels in compliance with the Trimaran Rules shall be steel and be in accordance with Rules for the Manufacture, Testing and Certification of Materials, July 2022 of the Complementary Rules. The use of other materials will be specially considered.

3.1.4  Service area. The service area of the vessel is to be defined in accordance with the Complementary Rules. If the Complementary Rules are the Rules for Ships, unrestricted service is assumed.

3.1.5  Vessel function. The vessel may be of any type allowed in the Complementary Rules. All statutory requirements appropriate to the vessel must be complied with.

3.2.1 The scantlings determined from the formulae provided in the Rules assume that the materials used are selected, manufactured and protected in such a way that there is negligible loss in strength by corrosion.

3.2.2 If the Complementary Rules are the Rules for Naval Ships or the Rules for Special Service Craft, all requirements calculated according to the Complementary Rules are consistent with this 'net' scantling approach.

3.2.3 If the Complementary Rules are the Rules for Ships then the local scantling requirements calculated according to the Rules for Ships include a corrosion margin. This margin may be removed by reducing the Rules for Ships plating thickness requirements by 10 per cent and stiffener scantlings by five per cent.

3.2.4 Where steel is not protected against corrosion, by painting or other approved means, the scantlings may require further consideration.

3.2.5 In the absence of a specific requirement from the Owner, the following corrosion margins are to be applied to net scantlings calculated by these Rules regardless of the type of corrosion protection fitted:

• +0,5 mm to all plating below a line 1,0 m above the design waterline;
• +2,0 mm to the keel plate.

3.2.6 Consideration should also be given to the addition of a corrosion margin to the following areas:

• Plating and stiffening at the lower edge of bulkheads bounding wet spaces.
• All tanks containing corrosive fluids and areas where spillage of corrosive fluids could occur.
• All uncoated structures.

3.2.7 If applicable, ships with a corrosion margin will be eligible for an enhanced scantling notation in accordance with the Complementary Rules.